A common arrangement for controlling the flow of fluid from a container is to use a valve that can be opened and closed by hand. It frequently happens that the valve cock of such a valve is left open, carelessly or on purpose, to allow the fluid to discharge while the operator is attending to other work. If the pressure within the container falls sufficiently while the valve cock is open, because the container has been emptied or for other reasons, it is possible for impurities to intrude into the container through the open valve cock. The impurities, such as outside air, dirt, oil, fumes and the like, can cause contamination of any fluid remaining within the container, or of the container itself. When this occurs, the container may need to be purged, with the remaining fluid removed either by substitution or perhaps vacuum suction and, in some instances, cleaning of the container itself may be required before it can again be placed in use. These curative procedures are costly in both time and labor.
In order to solve this intrusion problem, many proposals have been made, among which a seemingly effective approach is to provide the container with a check valve capable of closing in response to a reduction of pressure within the container below a preselected value. This can avoid a possible intrusion of outside, contaminating foreign matter into the container while it is being emptied; one pressure responsive valve for this purpose being the subject of U.S. Pat. No. 3,809,117. While the valve of this patent constitutes an advance in the art, it nevertheless leaves some aspects of the problem unsolved.
A valve unit used to solve the problem of intrusion should be designed so that the container can be easily filled with fluid through the valve and, at the same time, it must be designed to open properly for emptying fluid and close when pressure within the container falls below a preselected value. Further, it is desirable that the pressure-responsive valve unit be designed so that its operating pressure can be preset before it is installed on the container; the unit should lend itself to easy disassembly and repair. No pressure-responsive valve heretofore proposed for container use has successfully solved all of these problems and, thus, the need for an improved pressure-responsive valve exists. The present invention is intended to satisfy that need.